1. Field of the Invention
The invention relates to a transparent substrate, especially made of a rigid mineral material such as glass, coated with a thin-film multilayer that includes a functional layer of the metallic type able to act on solar radiation and/or long-wavelength infrared radiation.
The invention more particularly relates to the use of such substrates in the manufacture of improved thermal insulation glazing units having a high solar factor, and therefore mainly intended for cold climates. These glazing units are more particularly intended to equip buildings, especially with a view to making the building easier to heat in winter (“low-E” glazing units) and maximizing solar heating, which costs nothing.
In such improved multiple thermal insulation glazing units, substrates are kept a certain distance apart by spacers so as to define a cavity that is filled with an insulating gas, which may possibly be air, argon or krypton. A double glazing unit therefore comprises at least two substrates, for example glass sheets, separated pairwise by a gas-filled cavity. Thus, for example, the sequence 4/12/4 denotes a double glazing unit composed of two 4 mm-thick glass sheets and a 12 mm-thick gas-filled cavity and the sequence 4/12/4/12/4 denotes a triple glazing unit composed of three 4 mm-thick glass sheets and two 12 mm-thick gas-filled cavities.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Conventionally, the faces of a multiple glazing unit are numbered starting from outside the building. A double glazing unit thus comprises 4 faces, face 1 lying outside the building, face 4 lying inside the building and faces 2 and 3 lying inside the double glazing unit. Likewise, a triple glazing unit comprises 6 faces, face 1 lying outside the building, face 6 lying inside the building, faces 2 and 3 lying on each side of the first gas-filled cavity, inside the triple glazing unit, and faces 4 and 5 lying on each side of the second gas-filled cavity, inside the triple glazing unit.
These substrates may moreover be integrated into glazing units furthermore having particular functionalities, such as for example heating glazing units or electrochromic glazing units.
A thin-film multilayer known to provide substrates with such thermal insulation properties consists of a functional metallic layer having infrared-reflection and/or solar-radiation-reflection properties, especially a functional metallic layer based on silver or a silver-containing metal alloy.
In this type of multilayer, the functional layer is thus located between two antireflection coatings, each coating in general comprising a number of layers that are each made of a dielectric material, such as a nitride type, and especially silicon or aluminum nitride type, or an oxide type. From the optical point of view, the aim of these coatings that flank the functional metallic layer is to make this functional metallic layer “antireflective” in the visible range, so as to preserve a high transmission in the visible range.
A blocker coating is sometimes interposed between one or each antireflection coating and the functional metallic layer. The blocker coating located under, in the substrate direction, the functional layer protects said layer during any possible high-temperature heat treatment, such as bending and/or tempering, and the blocker coating located on the functional layer, opposite the substrate, protects this functional metallic layer from degradation liable to occur during the deposition of the upper antireflection coating and during any possible high-temperature heat treatment, such as bending and/or tempering.
It is known to use two dielectric layers having a refractive index near 2 (conventionally measured at a wavelength of 550 nm), for example a silicon nitride (Si3N4) layer surmounted by a mixed tin zinc oxide (SnZnOx) layer, above the functional metallic layer to make the functional metallic layer antireflective.
However, a triple glazing unit provided with such multilayers has a limited solar factor and/or has a yellow/green color, in particular in transmission, which cannot be judged to be sufficiently neutral.
There is therefore a need for a transparent substrate provided with a thin-film multilayer, the thin-film multilayer comprising a metallic layer having infrared-reflection properties, located between two, subjacent and superjacent, nonmetallic dielectric coatings, thereby allowing the solar factor of a multiple glazing unit provided with the substrate to be increased, and an acceptable color, especially in transmission, which is in particular less green, even also less yellow, to be obtained for the multiple glazing unit.